Television system



Dec. 19, 1933. H. M. DOWSETT 1,939,805

TELEVISION SYSTEM Filed March 18, 1952 2 Sheets-Sheet l INVENTOR H .M DOWSETT b BY ATTORNEY Dec. 19, 1933. DQWSETT 1,939,805

TELEVI S ION SYSTEM Filed March 18 1932 2 SheetsSheet 2 INVENTOR H.1"I. DOWS TT BY 1%; M(/&/

ATTORNEY Patented Dec. 19, 1933 PATENT; OFFICE TELEVISION SYSTEM Harry Melville Dowsett, Winchmore Hill, London, England, assignor to Radio Corporation of America, a corporation of Delaware Application March is, 1932, Serial No. 599,709,

- and in Great Britain March 23, 1931 1 Claim. c1. 178-6) This invention relates to television and like" systems and more particularly to scanning apparatus for use in such systems. It has already been proposed to televise large picture or scene by television as though it were a plurality of pictures or scenes; that is to say, the wholepicture or scene is sub-divided into a predetermined plurality of smaller constituentpictures or scenes, and these smaller pictures or scenes are scanned each by a separate scanning lightspot or equivalent means, the resultant electrical outputs due to the plurality of scanning operations being transmitted in multiplex. Such a system offers certain disadvantages the most important being that accurate lining up is necessary in order that the plurality of received smaller pictures or scenes shall be combined to make an apparently undivided larger picture or scene and that the -Zamplifiers in the various channels must be accurately matched in order that the reconstructed picture shall be of relatively correct intensity in the various sections.

The present invention has for its principal object to provide a television system whereby a large picture or scene may be satisfactorily televised without employing anundue width of frequency band per channel while'the number of pictures per second is maintained above the re- .quired minimum and whereby the disadvantages occurring with existing known systems are avoided.

According to this invention, a large picture or scene to be televised is scanned by a plurality ..of light spots or equivalent exploring scanning means, said exploring scanning means being caused to explore the whole picture or scene area simultaneously and at the same speed, and to explore different parts of that area at the same time; that is to say, each exploring scanning means is displaced relatively to the others. For example, a picture or scene may be scanned by three spots of light moving at the same speed, but so arranged relative to one another .that when the third light spot is at the end of the picture, the second is at about the middle, and the first is near the beginning.

The invention is illustrated in the accompanying drawings which show schematically .Itwo transmitting arrangements in accordance therewith.

In Figure 1 which shows one way of carrying out the invention, a scanning system, somewhat similar to that described in the specification accompanying the copending British application No. 3869/31 is employed and adapted or modified for the purposes of this invention.

Referring to Figural, 1 is a source of light the light from which is concentrated by a reflector 2 and passed through a condenser lens system 3 and a cylindrical lens system 4 to fall upon-one face of a prism 5 which is arranged within a drum or flanged disc 6 which drum has a plurality of apertures 7 whose centres are arranged along a single circumferential line of the drum, such circumferential line lying in a plane at right angles to the axis of the drum. Light is reflected by the prism 5 to pass through the apertures of the apertured drum whence it is projected by a projector lens 8 upon a mirrored drum structure 9 carrying or formed with three co-axial rings of mirrors 9a, 91), or 90 thereon.

The mirrors upon the mirrored drum structure 9 are all equal to one another and arranged in three rings 9a, 9b, 9c as shown, the mirrors of each ring lying tangential to the surface of an imaginary cone. The three cones have a common axis (the axis of the drum structure) and are of different angles, the mirror arrangement being such that light is reflected thereby in the form of three beams as shown. These beams are reflected from a common fixed mirror M in such manner that three scanning spots are projected upon the picture surface or scene P. The common axis, of the mirrored drum structure 9 is at right angles to the axis of rotation of the apertured drum 6, the apertures 7 in the latter drum being equally spaced at an angular distance apart equivalent to one dimenapertured drum and the arrangement is such that light projected through the apertures 7 swings across the mirrors of the mirrored drum structure, and is reflected therefrom via the mirror M on to the picture or scene which is to be scanned. Thus three scanning light spots are projected upon the picture or scene P. The arrangement is such that the whole of the picture or scene area is in turn scanned by the three light spots in a plurality of parallel lines as indicated the three drums in the mirrored drum structure 9 being arranged as shown so that at any instant of time the three light spots are at different parts of the whole picture or scene P. Light reflected from the three. scanning spots upon the picture or scene is caused to fall upon three corresponding mirrored drums 10a, 10b

from which further structure the reflected light is projected to fall upon three scanning photoelectric cells or equivalent devices 11, each proper to a different transmission channel.

Obviously, the apertured drum can, if preferred, be replaced by an apertured disc or mirror wheel constructed to perform a similar function and obviously the apertured drum may be replaced by a lens drum.

In the modification shown in Figure 2 the apertured drum is dispensed with. In this modification light from the source 1 and concentrated by the reflector 2 is projected by three cylindrical lens systems 4a, 4b, 40 upon one face of a prism 3f whence the light is' reflected through the apertures of a fixed apertured plate 12 and thence through three projection lenses 13a, 13b, 13c upon a mirrored drum structure 14, which drum structure consists in efiect of three so-called Weiller mirror wheels 14a, 14b, 140, said mirror wheels having their mirrors arranged in manner well known per se to give a scanning effect. The three mirror wheels incorporated in the drum structure 14 are so arranged that each of the three spots of light from said wheels scan the whole of the picture area P, said wheels being in eflfect displaced with reference to one another so. that the three spots of light are at different parts of the-picture area at the same time as is indicated in the figure. The scanning drum structure 10 of the arrangement of Figure 1 is replaced by a drum structure 15 which, like the drum structure 14, consists in efiect of three so-called Weiller mirror wheels 15a,'15b, 15c arranged in corresponding manner and 100 in a further mirrored drum structure 10 to the mirror wheels 14a, 14b, 14c incorporated in the structure 14.

Having now described my invention, what I claim and desire to secure by Letters Patent'is the following:

A television scanning system comprising a source of light, a first scanning member constituted by an apertured drum having a plurality of apertures arranged in a plane at right angles to the axis of rotation thereof, a reflector arranged within said drum and positioned to reflect light from the source through the apertures of the apertured drum, a second scanning member consisting of a plurality of mirror wheels driven together and at the same speed said mirror wheels being arranged in rings and rotating about an axis substantially at right angles to the axis of rotation of the apertured drum, means for projecting light reflected from the mirror wheels upon a picture surface or scene, and a third scanning member similar to the second scanning member and driven therewith, said third scanning member being arranged to reflect modulated light from the picture or scene upon the photoelectric cells or equivalent translating means, the first scanning member being driven at a considerably higher speed than the second and third scanning members, and the whole arrangement being such that light from the first scanning member is caused to sweep across the mirrors on the second scanning member whereby the picture is scanned simultaneously and over its whole area by a plurality of mutually displaced light spots.

HARRY MELVILLE DOWSETT. 

